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Effect of dietary lysine level on thyroid activity and body temperature in the chick Pastro, Kenneth Ralph


Experiments were conducted to study the effect of dietary lysine level on thyroid activity and body temperature in White Leghorn cockerel chicks. Thyroid activity was measured in birds 4-to-5 weeks of age and body temperature was measured in birds 4-to-8 weeks of age. Three diets based on corn and sesame meal and containing 20% protein and 0.64% (basal diet), 1% (control diet) or 2% of L-lysine respectively were used. These diets contained deficient, optimal and excessive amounts of L-lysine respectively. Thyroidal experiments were conducted at different times of the year. Thyroid activity was assessed by measuring the level of I¹³¹ in the plasma and thyroid or thyroid only at various times after an intravenous injection of 0.55 μc of I¹³¹ 100 gm of body weight. In August-September, thyroidal response to diet was investigated in birds fed the test diets for either 1 or 17 days prior to administration of I¹³¹. When the test diets were fed for 1 day prior to the injection of I¹³¹, data for per cent I¹³¹ per unit of thyroid weight and for the ratio of thyroidal to plasma I¹³¹ (T/P ratio) indicated that either a deficiency or an excess of dietary lysine enhanced thyroid activity. Feeding the test diets for 17 days appeared to attenuate the responses observed in the 1-day trial. In January, thyroidal response to diet was assessed in birds fed test diets either 1 day before or 3 days after the injection of I¹³¹ . Only the diets containing 0.64% and 1% of L-lysine were fed. When appropriate, 0.2% thiouracil was added to block thyroidal uptake of recycled I¹³¹. When all four diets were fed, I¹³¹ level per unit of thyroid weight and T/P ratio calculated from data obtained 5 minutes, 1 and 3 hours after I¹³¹ administration indicated that dietary lysine deficiency under the circumstances of the experiments reduced thyroidal uptake of the isotope. When I¹³¹ was injected 3 days prior to imposition of the test diets, the values for I¹³¹ per unit of thyroid weight after the feeding trials started indicated that the lysine deficiency reduced the rate of release of thyroidal I¹³¹. In a further experiment, levels of thyroidal I¹³¹ measured 5, 10, 24, 48, and 72 hours after I¹³¹ injection verified that the lysine deficiency reduced thyroid activity. In March, the effect of ambient temperature on thyroidal response to dietary lysine level was investigated. Thyroidal I¹³¹ was measured 6 hours after I¹³¹ administration to birds which had been fed the deficient diet for 1 day. Dietary lysine level and environmental temperature had an interacting effect on total thyroidal I¹³¹ and per cent I¹³¹ per 100 gm of body weight. Under the conditions of the experiment, lysine deficiency enhanced I¹³¹ uptake in a warm environment but has no effect or depressed activity in a cold environment. Temperatures were measured with thermistor probes inserted into the cloaca, the brain and the pectoral is muscle. When fed for either 18-to-30 hours or for 2 weeks, the lysine deficient diet increased muscle temperature. The diet had no apparent effect on brain or cloacal temperature but detection of a response may have been obviated by the technique used to measure temperatures in these two locations. Feeding sub-optimal or excessive levels of dietary lysine for only 1 day caused a change in thyroid activity. In a warm environment, both sub-optimal and excessive levels of lysine enhanced thyroid activity. Environmental temperature appeared to modify the thyroidal response to dietary lysine level. In a warm environment, a deficiency of lysine increased muscle temperature.

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